Assessment on Abrasiveness of Rock Material on the Wear and Tear of Drilling Tool Edy Tonnizam Mohamad Senior Lecturer (Dr.), Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor
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Rosli Saad Senior Lecturer (Dr.), School of Physics, Universiti Sains Malaysia, Penang, Malaysia;
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Nor Nazrin Binti Hamzah Postgraduate Student, Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor
Siti Norsalkini Mohd. Akip Tan Postgraduate Student, Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor
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Maybelle Liang Postgraduate Student, Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor
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ABSTRACT An assessment of rock material was carried out in this study to determine the wear resistances of drill bit due to physical properties of granite and old alluvium. This study intends to provide a current stateof-the-art comparison of petrographical analysis and interpretation of F-Schimazek’s value in terms of its drillability rate and the wear and tear of the drilling tools. Rock samples representing the drilling locations were collected and tested for its physical and mechanical properties in the laboratory. The FSchimazek’s value is obtained from a number of easily measured parameters namely Brazilian Tensile Strength, mineralogical composition and grain size. In this study, samples of old alluvium were collected from drilling project prepared for blasting work from an interchange project at Gelang Patah, Johor, Malaysia. Besides that, samples of granite were collected from Maktab Rendah Sains Mara (MRSM) Project at Bandar Sri Alam, Masai, Johor for the same purpose. The results are then analyzed with the rate of penetration measured during the drilling work. The result shows a good relation between the parameters involved and the methods are simple and practical to be employed for the drilling assessment.
KEYWORDS:
content
Wear of drilling tools, petrographic properties, F-Schimazek’s value, quartz
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INTRODUCTION Percussive drills are used extensively in open pit mines and quarries. Its drillability mainly depends on operational variables and rock characteristics. An accurate estimation of drilling rate helps to plan the rock excavation projects more efficiently. Among parameters of rock that influence drilling works are rock hardness, rock texture and density, rock fracture pattern and general structure of the formation or rock mass (Thuro, 1997). Term of rock drillability means the ease of drilling a hole in the rock mass. Studies show that the drillablity of rock and thereby the penetration rate of a drill are affected by rock hardness, rock texture and density, rock fracture pattern and general structure or the formation or rock mass (Deketh, 1995 & Arthur, 1996). According to Thuro (1997), during the past years in conventional drill and blast tunneling, issues arise in accurate prediction of drillability in rock. The drillability is not only decisive for the wear of tools and equipment but is also with the drilling velocity that is a standard factor for the progress of excavation works. Previous study shows that, one of the main issues associated with the rock cutting tools is the unknown relationship between the cutting tools with types of rock and geological factors. There are many parameters affecting the drillability of rock cutting tools such as rock hardness and strength. If the parameters cannot be predicted, it may cause unexpected high rates of wear to the cutting tools which lead to increases of project cost and budget (Deketh, 1995). If the abrasiveness of rock cannot be predicted, may cause to unexpected high rates of wear of tools and results in high financial losses that can impact the budget of a project. Therefore, it is important to determine the abrasiveness of the rock materials and evaluate the productivity of drilling rate, wear and tear of drilling bits in order to predict and minimize the cost of the cutting tools. The result of the study is not only to evaluate the drilling performance, but also as a good indicator in tunneling and normal excavation process.
GEOLOGY There are two study areas which located at Gelang Patah, Johor Bahru and Bandar Seri Alam Masai. The geology map for both sites is shown in Figure 1. These sites are chosen because drilling works are in progress during the study period. Figure 2 shows site condition at Gelang Patah which consist of old alluvium which is hard and sample can only be broken by a hammer blow into silty sand. The feldspar and quartz minerals in alluvium undergo weathering process, transform slowly into clays and dissolved silica. On the other hand, Figure 3 shows an overview of Seri Alam's site which underlain by coarse grained granite. Quartz and feldspar are the essential materials. Quartz form 25 to 40 per cent of the rock while feldspar up to 50 per cent or more. Other materials present in granite are mica, hornblende, augite and tourmaline; soda-rich minerals such as reibectite. The specimens are in light colour with a white or pink tint according to the color of the feldspar, and are coarsely crystalline (Blyth, 1974).
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Figure 1: Geology Map of Site Location
Figure 2: An overview of site at Gelang Patah which consist of old alluvium
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Figure 3: An overview of site at Bandar Seri Alam which consist of granite
FIELD AND LABORATORY STUDIES This study include field and laboratory study. The field study involves examination on the rate of drilling and measurement of wear and tear of the drill bit by weighing of it after 50 meter of drilling. The type of drill bit and the speed of drilling are maintained to be similar at both sites. The laboratory works include measurements of Brazilian Tensile Strength and petrographical analysis in order to derive the F-Schimazek’s value. Brazilian test is the most widely used instruments because of its relative simplicity and reliability of the results obtained (Figure 4). It is used to determine the tensile strength R t for rocks and rock-like materials. There are two standards presented for Brazilian test that are GOST 21153.3-75 Alfred (1983) and ISRM (1987). The basic parameters are shown in Table 1 (George, 1995). For the GOST method, the value of m must always ≤ 0.1D, and this cause failure to occur from the contact areas. The ISRM method creates incomparably better test conditions.
Figure 4: Brazilian test apparatus
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In this study, method GOST 21153.3-75 is being used for Brazilian test. The tensile strength of each specimen is calculated using this formula: σt = 0.636 P Dt
(1)
where, P is the load at failure (N) D is the diameter of the test specimen (mm) t is the thickness of the test specimen measured at the centre (mm).
Table 1: Standard for the Brazilian test (George, 1995) Test parameters
GOST 21153.3-75
ISRM 1978
Specimen diameter D,mm
40-50
>54
Diameter to thickness ratio L/D
1-0.1
0.5
Measuring exactness of the sizes, mm
0.1
-
Roughness in the contacts, mm
0.4
0.025
Roughness in the walls, mm
0.4
0.25
Deviation from perpendicular
1 mm
0.25o
Loading devices
Platens
Cylinders*
0.1-1 MPa/s
15-30**
>10
>10
R = 0.64 P/DL
R = 0.636 P/DL
Loading rate Number of specimens Calculation formula
The abrasiveness properties of rock were determined by using F-Schimazek’s Value. The value represents the abrasiveness of rock towards the tool or cutter wear that used in the excavation work. This index can be evaluated as equation below (Schimazek and Krantz, 1970):
where,
F = [ EqQtz x Ø x σt ] / 100
(2)
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F is the Schimazek’s abrasiveness factor in N/mm unit EqQtz is the percentage quartz or any other equivalent mineral ø stands for the quartz grain size in mm. Gehring (1977) reported that if the grain size is less than 0.025 mm, then the effect of the grain size to the abrasiveness is not significant. If the rock does not consist of any particle of quartz, then the above equation cannot be used. σt is the average of Brazilian tensile strength of the rock which represents the interlocking between particles that influence the cutability and abrasiveness. F-Schimazek’s value gives a linear relationship towards the abrasiveness of the rock (Peter, 1993). The higher the F-Schimazek’s value, the more abrasive is the rock and vice versa. The classification of abrasiveness by using the F-Schimazek’s Value as proposed by Arthur (1996) is shown in Table 2.
Table 2: The classification of abrasiveness for rock materials (Arthur, 1996) Nomenclature
Class
F-Schimazek’s Value
Extremely abrasive
1
> 11
Very abrasive
2
5 - 11
Moderately abrasive
3
2-5
Slightly abrasive
4
0.5 -2
Non-abrasive
5
< 0.5
RESULTS AND DISCUSSION The results are presented in two sections: laboratory and field result. The result for laboratory includes Brazillian Tensile Strength Test and petrographic test (macroscropic and microcrospic examination). In order to determine the influence of the wear of drilling bits, the weight of the button bits were measured at every 50 meter of drilling at the site. For a better presentation of the results, a graph of percentage of tool wear versus drill length is plotted as shown in Figure 7. Results for Laboratory Study Petrographic Analysis The results consist of both macroscopic (Table 3) and microscopic (Table 4) descriptions. The results are summarized as follows.
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Table 3: Results of macroscopic study on the sample Type of Rock Old Alluvium
Granite
Details On Macroscopic Study The material is light grey to yellowish in color and has very fined to medium sized grained with size of 1 mm. This material is categorized as old alluvium (sandstone) and considered as highly-moderately weathered (grade III-IV). The rock is light grey in color with a few spotted of dark mineral. The grains are considered medium-grained in size, ranging in the type of specimen from about 1 to 2 mm and well interlocked. The rock is categorized as intrusive or plutonic igneous rock (weathering grade III).
Table 4: Results of microscopic study on the sample Type of Rock Old Alluvium
Granite
Details On Microscopic Study The material is categorized as fine-grained sandstone with fine grained, dense, generally, tightly interlocked structure with a mixture of platy minerals and quartz grains (Figure 5). Mineral composition: Under the thin section, the material is composed of: Quartz : ~ 85 % Rock Type : The rock is categorized as intrusive or plutonic igneous rock. The textures of the rock are Holocrystalline, medium-grained and hypidiomorphic equigranular. (Figure 6). Mineral composition: Under the thin section, the rock is composed of: Alkali feldspar and plagioclase feldspar : ~ 55-60 % Quartz : ~ 30-35 % , Biotite : ~
